Coatings have long been available which adhere to a wide variety of metals including for example, cold rolled steel, hot-dipped galvanized steel, electrogalvanized steel and aluminum and anodized metal, particularly anodized aluminum. The coil coatings and industrial coatings industries, for a number of years, have successfully coated unsealed, anodized metal substrates which have been anodized by an electrochemical process employing sulfuric acid, chromic acid, phosphoric acid, or oxalic acid electrolytes. Such unsealed, anodized metal substrates provide an excellent base for adhesion of a paint, enamel or lacquer coating because of the porosity of the anodized metal surface. Clear methacrylate lacquers have been known for years to be useful to paint such unsealed, anodized metal surfaces to provide a high gloss coating.
It has also been known to seal such anodized metal substrates where it is desired to employ the metal in an environment where the porosity f the anodized metal is undesirable, such as for example when used in auto trim parts where exposure to the elements can result in corrosion or staining of the metal. Sealing of such anodized metal substrates, such as by immersion in boiling deionized water, sodium bichromate, nickel acetate solutions or steam, makes the anodized coating on the metal nonabsorptive by closing down or plugging the pore structure of the anodized coating. Additionally, sealing of the anodized metal substrate can substantially reduce the abrasion resistance thereof. When anodized metal substrates have been sealed, it is very difficult for a paint to adhere to the surface of the sealed, anodized metal substrate. The problem is exacerbated when it is desired to coat untreated bright, sealed, anodized metal substrates, particularly untreated, bright, sealed, anodized aluminum substrates.
Furthermore, in producing bright, unsealed, anodized metal parts for use as auto trim and the like, it has been necessary to first fabricate the desired part, then anodize the metal substrate before applying a high gloss coating to the anodized metal part. The part forming process would result in cracking and delamination due to lack of sufficient adhesion of the high gloss coating if said coating were applied before the part fabrication step. Moreover, the clear methacrylate lacquers employed for the high gloss coating are generally spray painted onto the prefabricated part and air dried since long baking times typical of spray coatings would discolor the anodizing. As stated hereinbefore, such problems are magnified many times over when it is desired to provide a high gloss coating on bright, untreated, sealed, anodized metal substrates and therefore it has not been possible to successfully coat such metal substrates in coil form and thereafter fabricate parts from the coated metal coil substrate.
Currently the metal employed in such automotive trim parts is stainless steel. It would be especially desirable if said stainless steel parts could be replaced with untreated, bright, sealed, anodized aluminum since the latter substantially reduces galvanic corrosion compared to the former. Thus, it would be highly desirable to be able to coat untreated, bright, sealed, anodized aluminum substrate in coil form with a high gloss coating and to be able to thereafter fabricate parts therefrom.
Additionally, even if one were able to coat untreated, bright, sealed, anodized metal substrate in coil form with a high gloss coating, it is also necessary that the coated coil not become blocked, i.e. that the coated coil is able to slide and unroll without sticking and binding. Furthermore, such a coating must be high gloss, i.e. produce at least 80 percent reflectance at a 60.degree. angle.
It is therefore an object of this invention to provide a high gloss coating composition and the use thereof for coating untreated, bright, sealed, anodized metal substrates and more particularly to coat such metal substrates in coil form. A further object of this invention is to provide such a high gloss coating composition and process for coating such metal substrate whereby the resulting coating has sufficient integrity and adhesion to the metal substrate, particularly coiled metal substrates, to permit post-coating fabrication of the coated metal into suitable parts or elements, particularly parts or elements for use on automobiles. Another object of this invention is to provide such coatings which also exhibit sufficient stability and integrity to permit such high gloss coated metal substrates to resist corrosion, hazing, cloudiness, flaking, cracking, mottling and/or delamination of the coating when exposed to environmental factors such as salt, ultraviolet light and excessive heat.
A still further object of this invention is to provide a high gloss coating composition for such metal substrates which avoids problems with the composition gelling during extended periods of storage at elevated temperatures up to about 120.degree.-140.degree. F. (49.degree.-60.degree. C.) prior to use in the coating process since such temperatures are commonly encountered in and around coil coating plants. Yet another object of this invention is to provide a high gloss coating composition for coating such untreated, bright, sealed, anodized metal substrates for producing high gloss coating on said substrates which coating is capable of having indicia printed therein, such as by a sublimation printing process. Another object of this invention is to provide such high gloss coated metal substrates capable of having elastomeric polymeric or rubber material bonded thereto, such as for example, the elastomeric material bonded to bright metal trim around automobile windows. It is still another object of this invention to provide a high gloss coating composition for coating untreated, bright, sealed, anodized metal substrates having a low coefficient of friction for slippage and mar resistance and to aid in forming the coating by ensuring adequate flow and levelling of the coating composition during the coating process.